Wash. Rev. Code § 26.26A.430
(1) A proceeding to determine whether an alleged genetic parent who is not a presumed parent is a parent of a child may be commenced:
(2) Except as otherwise provided in RCW 26.26A.465, this subsection applies in a proceeding described in subsection (1) of this section if the woman who gave birth to the child is the only other individual with a claim to parentage of the child. The court shall adjudicate an alleged genetic parent to be a parent of the child if the alleged genetic parent:
[ 2018 c 6 s 507.]